I served in the military for 30 years. But it was impossible to fully understand the sacrifices of our troops and their families until April 29, 2007, the day my son, First Lt. Travis Manion, was killed in Iraq.

Travis was just 26 years old when an enemy sniper's bullet pierced his heart after he had just helped save two wounded comrades. Even though our family knew the risks of Travis fighting on the violent streets of Fallujah, being notified of his death on a warm Sunday afternoon in Doylestown, Pa., was the worst moment of our lives.

While my son's life was relatively short, I spend every day marveling at his courage and wisdom. Before his second and final combat deployment, Travis said he wanted to go back to Iraq in order to spare a less-experienced Marine from going in his place. His words—"If not me, then who . . . "—continue to inspire me.

My son is one of thousands to die in combat since the terrorist attacks of September 11, 2001. Because of their sacrifices, as well as the heroism of previous generations, Memorial Day 2012 should have tremendous importance to our entire nation, with an impact stretching far beyond one day on the calendar.

I’ve known the Manion family for three years. I met them six months after Travis died, when 200 of his family members and friends came to Washington to run the Marine Corps Marathon in his honor. Travis had planned to run the race with his dad when he got back from Iraq. Instead, his father ran the race that day wearing two numbers. The official results say Travis Manion crossed the finish line at 4:19:39.

Back then, his mother Janet was barely able to speak at a pre-race dinner honoring Travis. This year, she virtually emceed the event. His older sister went from grieving her brother to leading a foundation in his honor. His father went from being a seemingly stoic, mostly silent, Gold Star father to a candidate for Congress in 2008, outperforming expectations in a tough Pennsylvania district and a bad year for Republicans, but ultimately losing to antiwar Iraq veteran Patrick Murphy.

Each member of the family has changed. Where they used to say “Since Travis . . . ,” trailing off without finishing the sentence, they now say “Since we lost Travis,” with affection and purpose. But beyond grieving, they’ve committed themselves to the mission Travis is no longer here to serve—the good of his fellow veterans, his country, and the people of Iraq.